1. Field of the Invention
This invention relates to a novel asbestos product, its method of manufacture and its use as a reinforcing agent.
2. Brief Description of Prior Art
Asbestos has been on the commercial markets of the United States for over 100 years. Initially the fibers were simply a curiosity. As its fire retardant capabilities became more widely recognized, it became a flame safety ingredient in fireproof curtains, walls, clothing and shingles. However, the commodity really came into its own with (1) the widespread electrification of industry and (2) the growth of the American automotive companies. In the former, the superior electrical insulation properties of low iron chrysotile asbestos were recognized; the latter acknowledged the ability of the fibers to impart some of their inherent strength to friction components--i.e. brakes--while under thermal stress. Still later, the growth aspects of the asbestos industry focused on the utilization of fiber in connection with plastics. At present, over 800,000 tons of asbestos fiber is consumed annually in the United States in over 3,000 applications. In most of these applications, asbestos is a key ingredient and few substitutes are currently available.
The word asbestos is a broad generic term that has been accepted and applied to a number of fibrous mineral silicates found in nature. As a group, they are incombustible and can be separated by mechanical means into fibers of various lengths and thicknesses, but have differing chemical compositions and other properties. Generally speaking, six varieties of asbestos are recognized: (1) chrysotile, the finely fibrous form of serpentine and five others all of the amphibole group, (2) anthophyllite, (3) crocidolite, (4) tremolite, (5) amosite, and (6) actinolite. Of the foregoing, chrysotile constitutes about 94% of the current world production of asbestos and this percentage is increasing.
The common property of the asbestos minerals is that they have physical characteristics similar to those of organic fibers yet they are both non-combustible and noncorrosive. If sufficiently long to be spun, the fibers of chrysotile and crocidolite are woven into fabrics with wide application. Among the advantages of chrysotile, which set it apart from the amphiboles, are world-wide availability, mechanical strength, flexibility, positive surface charge, low iron content, softness, a low refractive index and general resistance to the elements of the air.
Traditionally, the uses of asbestos are largely determined by the characteristics, particularly length, of a given fiber. Also by tradition, the Quebec Grading System is the most widely followed system of valuing fiber. Other producing areas and countries use differing terminology for the various grades, but this amounts to little more than paraphrasing the Quebec system. All uses of asbestos are as processed fiber. The processed chyrsotile fibers are placed into the following groupings, which are based upon length of fiber.
Groups 1, 2, and 3--These groups are composed of the longest fibers; the major end use products include textiles, clothing, theatre curtains, different types of packings, in the manufacture of fire-proof textile products, woven brake linings, clutch facings, electrical insulation materials, and high pressure and marine insulation.
Group 4--Its major use is in asbestos cement pipe, used in the transportation of water, as in municipal water works, irrigation and conservation projects.
Group 5--This group is used in asbestos cement sheets, flat corrugated sheets, low pressure asbestos cement pipes, and molded products; it is also used in some paper products such as pipe insulation, wrappings, and other products, including brake linings and gaskets.
Group 6--The main consumption for this group is the asbestos cement products mix, gaskets, brake linings, vinyl sheet backings and millboard.
Group 7--The group is used in molded brake linings and clutch facings, as a filler in vinyl and asphalt floor tile, in asphalt compounds, joint and insulation cements, roof coatings, plastics and caulking compounds.
If such a generalization is possible, the "typical Quebec type" asbestos occurs as cross fiber veins ranging in width from microscopic dimensions to more than 6 inches in which the fibers lie approximately perpendicular or somewhat inclined to the walls. In place the "typical Quebec type" chrysotile appears pale green to greenish yellow in color. It is only when separated that the fibers form the fluffy white mass most of us associate with asbestos.
Generally the ore bodies in Quebec contain 5 to 7 percent fiber, although at some deposits, rock that contains a little as 1.5 or 2 percent is worked if substantial fiber length is present. The veins are irregularly distributed in the deposit so that normally about 20 percent or more of the rock mined is barren and discarded as waste. Consequently, the mill feed, at most mines, contains about 7 to 8 percent fiber.
In general, the commercial value of a "typical Quebec type" asbestos deposit in massive serpentine is determined by balancing a number of factors including the fiber content of the rock, proportions of the various fiber lengths and volume of fiber bearing rock. The fiber content of the rock, which depends on both the width and spacing of the veins seldom exceeds 5 percent. The bulk of the fiber in most of the world's deposits is less than 1/4" in length and thus is of relatively low value. This ore must contain sufficient values to cover mining costs (stripping, drilling, blasting and excavation) and milling via the complicated procedure necessary to extract a clean fiber from the serpentine. There are many "typical Quebec type" asbestos deposits in the world but few measure up to the stringent requirements of an economic ore body.
There is also known to exist in at least two parts of the world, i.e. the Coalinga area of California and the Stragari mine in Yugoslavia, asbestos ore bodies which in physical appearance are markedly unlike almost any other asbestos ore in the world. The veining that characterizes "typical Quebec type" chrysotile asbestos is absent from the serpentine host and instead, the ore consists of friable masses of matted chrysotile flakes surrounding fragments of rock. The flexible flakes have been shown to be made of short fibered asbestos and petrographic x-ray and chemical analyses have shown the fibers to be chrysotile and identical to Canadian chrysotile. The main difference lies in the fact that the fibers, rather than occuring in vein form, are randomly oriented and matted into flakes.
Regardless of its nature or source, before the mined chrysotile asbestos can be used as a reinforcing agent, it is conventionally subjected to a heavy pretreatment plus a standard milling operation whereby the ore is successively dried, separated into individual fibers of a specific length by screening, opened by disc grinders and then packaged for marketing. Unfortunately, asbestos fibers separated from the deposits in the Coalinga area of California or the Stragari mine in Yugoslavia hereinafter referred to jointly as Coalinga type asbestos fiber are too short for many industrial and emergency uses. Short asbestos fibers are characterized by insufficient strength.